linux-kernel - Re: x86 memcpy performance

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Message-ID: <CAObL_7HAhSaknKRD=0BGWYdZaanX9fOc+i2B74K844T=1r6yGg@mail.gmail.com>
Date:	Mon, 15 Aug 2011 12:58:24 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	melwyn lobo <linux.melwyn@...il.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	borislav.petkov@....com
Subject: Re: x86 memcpy performance

On Mon, Aug 15, 2011 at 12:12 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 08/15/2011 08:36 AM, Andrew Lutomirski wrote:
>>
>> (*)  kernel_fpu_begin is a bad name.  It's only safe to use integer
>> instructions inside a kernel_fpu_begin section because MXCSR (and the
>> 387 equivalent) could contain garbage.
>>
>
> Uh... no, it just means you have to initialize the settings.  It's a
> perfectly good name, it's called kernel_fpu_begin, not kernel_fp_begin.

I prefer get_xstate / put_xstate, but this could rapidly devolve into
bikeshedding. :)

--Andy
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